The present invention relates to an electrode device used in microwave surgery apparatus, with which coagulation, hemostasis, ablation, etc. of biotissues is performed by means of microwave, and more specifically to an electrode device in which the direction of the electrode fixed at the distal end of an elongated shaft can be controlled at a proximal site of the shaft.
For treatment of pathological tissues, e.g., malignant tumors, which are located deep in a body, methods which have been widely applied are those by which the body is deeply cut open through the skin to expose the lesion and then the lesion is excised together with the adjacent tissues. In recent years, however, due to a trend for benefit of patients quality of life, treatment methods that do not involve abdominal section and could thereby shorten the term of hospitalization are becoming familiar. Among them, examples of methods for treatment of hepatocellular carcinoma include transcatheter arterial embolization (TAE), percutaneous ethanol injection (PEI), microwave coagulation therapy (MCT).
In microwave coagulation therapy, selective coagulation, hemostasis, ablation, etc. of the lesion are performed utilizing the dielectric heat generated in the bio-tissues due to a localized microwave electromagnetic field created between electrodes applied to the lesion site by radiating microwave at a predetermined frequency between the electrodes. It has advantages over coagulation or ablation procedures using an electric or laser knife in hemostatic and coagulation effects, as well as in its easiness of handling. For microwave coagulation for deep region of the body, there are known methods such as percutaneous microwave coagulation therapy (PMCT) and laparoscopic microwave coagulation therapy (LMCT). In laparoscopic microwave coagulation therapy, surgery is performed by creating in the abdominal surface multiple openings usually with a diameter of several mm at proper locations surrounding the umbilicus, then inserting, through respective trocars, through one of which a laparoscope with a CCD camera equipped at its distal end, through two of which forceps, and through another of which a surgical electrode, and introducing a nontoxic gas such as carbon dioxide into the abdominal cavity to inflate the abdomen, and then manipulating the surgical electrode from outside of the body while watching the image captured by the CCD camera and displayed on a monitor.
When the electrode is being inserted through the trocar into the abdominal cavity, the electrode and the supporting shaft used for laparoscopic microwave coagulation therapy must be in generally straight configuration. Thus, the conventional electrode has an integrally attached straight shaft and the direction of its electrode tip is fixed. On the other hand, the location of a lesion to be coagulated may vary even with regard to the same organ, and there are cases in which blood vessels or the bile duct not to be coagulated lie in front of the lesion. With a conventional electrode, which is attached to the supporting shaft in a fixed, generally straight configuration, therefore, it has often been difficult to apply the electrode at an optimal angle to the lesion.
To solve this problem, it is necessary to design an electrode such that, after insertion of it into the abdominal cavity, the direction of the electrode can be changed to a desired angle by operation at a proximal site. However, unlike an electric or laser knife, one of the characteristics of an electrode for microwave coagulation therapy is that it contains inside a microwave coaxial cable up to the distal end of the electrode. Due to this, there has been proposed no electrode usable in laparoscopic microwave coagulation therapy in which the direction of its electrode tip can be controlled at its proximal site.
That is, there is a difficulty with an electrode for microwave coagulation therapy in providing within its support shaft a complex mechanism for controlling the angle of the electrode, for a coaxial cable occupies main space in the cross section of the support shaft""s lumen.
In addition, it is one of the characteristics of a microwave coaxial cable that if there is a region curved at an acute angle, the microwave being conducted is partly reflected at the region to create a standing wave, thus causing generation of heat and a loss of energy, and the forward conduction of microwave energy beyond that region is eventually impeded. Therefore, even when the electrode is bent near its distal end, its curve must not be acute so that the curve of the interior coaxial cable can have as large a radius of curvature as possible.
Furthermore, a microwave coaxial cable extending contained within the shaft includes a inner conductor, an insulating medium covering the inner conductor, and an outer conductor surrounding the insulating medium. Thus, as a coaxial cable has substantial thickness and therefore resists deformation, a mechanism that can apply a sufficient force on it is required for bending it.
Furthermore, as the electrode is inserted into or pressed against a lesional tissue, the electrode must be so constructed that the angle of the electrode can be retained even when the electrode receives a reaction force from the tissue.
Still further, as tissue coagulation with microwave generally takes about 60 seconds per site, the electrode once applied to the lesion site must be held at the predetermined angle during the period. Therefore, it is preferable that the electrode is so designed that the angle is fixed without imposing extra burden on the hand of the operator once the direction of electrode is set at an desired angle.
In addition, further problem was noticed that while the support shaft containing a coaxial cable is being bent, the interior coaxial cable caused to curve is often distorted along the longitudinal axis, thus creating stress in the direction of the longitudinal axis, and this stress could prevent smooth bending of the shaft beyond a certain amount of bending.
The objective of the present invention is to solve the above mentioned problems and provide an electrode for microwave coagulation therapy, in which the direction of the electrode tip can be controlled as desired through operation at its proximal region.
The present inventors found that, according to a planned maximal angle with the distal end of the electrode, by separating the distal part of support shaft of the electrode into one or more links whose angles can be altered in a single plane, and arranging them so that the most distal one of the links can be pulled and pushed back on its deflection side from a proximal region by means of an elongated resilient member along the inner surface of the support shaft, the direction of the distal end of the electrode containing a coaxial cable can be easily and reliably controlled from the proximal region of the electrode, and, even where multiple links are included, all of the links can be moved in concert retaining their mutual balance and therefore an acute curve will not created in any region along the coaxial cable contained therein even when the angle of the electrode is changed a great deal.
Thus, the present invention provides an electrode device for microwave surgery which allows to control the angle of the electrode thereof comprising: a handpiece provided with a rigid hollow support shaft extending toward a distal end, a movable support provided at the distal end of the support shaft and carrying thereon an electrode for microwave surgery, a microwave coaxial cable which is connected at the proximal end thereof to a microwave coaxial connector and connected in the movable support to corresponding portions of the electrode for microwave surgery, said cable extending through the handpiece and the support shaft, wherein:
(a) the movable support comprises one or more links surrounding the coaxial cable and longitudinally connected to the distal end of the support shaft so that the movable support can be bent and stretched, in a single plane, between the direction of the longitudinal axis of the support shaft and a direction deflected therefrom, and
(b) the electrode device further comprises a resilient stiff member fixed at one end thereof to the deflection side of the most distal one of the links composing the movable support and so connected to a control section of the handpiece movable from outside that the resilient stiff member can be pulled and pushed back at the proximal end of the handpiece, said resilient stiff member extending through the support shaft.
In laparoscopic microwave coagulation therapy, the electrode device of the present invention in the above configuration can be kept stretched straight when being introduced into a trocar inserted into the abdominal cavity, and then, after a predetermined length of its distal part has been inserted out of the trocar into the abdominal cavity, can be manipulated as required, by operating the control section provided in the handpiece, to adjust the direction of the electrode tip to be adapted to the location of the lesion. In addition, although it depends on a mechanism by which both pulling and pushing force are applied only to the most distal one of the links, all of the links can be moved in concert while retaining their mutual balance, even where the movable support is composed of multiple links. Thus, concentration of curvature will not occur to a limited region of the movable support, and therefore creation of an acute curve will be avoided at any region along the coaxial cable contained therein even when the angle of the electrode is changed a great deal. With such configuration and functions, the present invention allows to control the direction of the electrode tip within the abdominal cavity as desired by proximal manipulation during microwave coagulation therapy, thereby enabling more flexible operation in accordance with the location of the lesion to be coagulated and with conditions of the surrounding tissues.
When changing the direction of the electrode tip greatly, depending upon the mutual positioning of the contained coaxial cable, the links and the support shaft, there may be cases in which the coaxial cable is strained or compressed along the longitudinal axis and thus created substantial longitudinal stress hinders a smooth manipulation of the electrode tip. To address this problem, the present inventors found that by arranging the coaxial connector positioned in the handpiece to be able to sift, e.g., slide, along the longitudinal axis within a predetermined range rather than fixing it to the handpiece, any conceivable stress along the longitudinal axis of the coaxial cable can be released and thus allowing a smooth manipulation of the electrode tip without being hindered even for a great deal of change in its angle of, e.g. up to 180xc2x0.
Therefore, the present invention further provides an electrode device for microwave surgery as described above and further characterized in that the coaxial connector is attached to the handpiece in such a manner that it can shift along the longitudinal axis within a predetermined range so that it can follow a longitudinal shift of the coaxial cable in association with the movement of the movable support between the deflected and the stretched positions.
With this additional feature, even when the angle of the electrode tip is changed a great deal by bending the movable support, no stress is created in the coaxial cable along its longitudinal axis because the coaxial connector, to which the proximal end of the coaxial cable is connected, may shift, e.g., by sliding, in the direction of the longitudinal axis relative to the handpiece in response to the longitudinal shift which may take place in the coaxial cable within the support shaft. Therefore, the angle of the electrode tip can be changed up to as much as 180xc2x0 without causing any problem.